This invention relates to a progressive cavity apparatus, and more particularly to drive trains for progressive cavity devices and to progressive cavity driving, drilling, and pumping apparatus.
The use of progressive cavity or single-screw rotary devices is well known in the art, both as pumps and as driving motors. These devices have a single shaft in the shape of one or more helix contained within the cavity of a flexible lining of a housing. The generating axis of the helix constitutes the true center of the shaft. This true center of the shaft coincides with its lathe or machine center. The lined cavity is in the shape of a two or more helices (one more helix than the shaft) with twice the pitch length of the shaft helix One of the shaft or the housing is secured to prevent rotation; the part remaining unsecure rolls with respect to the secured part. As used herein, rolling means the normal motion of the unsecured part of progressive cavity devices. In so rolling, the shaft and housing form a series of sealed cavities which are 180 degrees apart. As one cavity increases in volume, its counterpart cavity decreases in volume at exactly the same rate. The sum of the two volumes is therefore a constant.
When used as a pump, the unsecured part, whether shaft or housing, is rotated by external forces so as to roll with respect to the secured part. Fluids entering the housing are pumped through it by the progressing cavities. When used as a motor, the unsecured part, whether shaft or housing, rolls with respect to the secured part in response to fluids flowing through the housing. Whether the progressive cavity device is used as a motor or a pump, the part that is unsecured and free to rotate is known generally as the rotor and the secured part is known generally as the stator. Optimum performance is obtained when movement of rotor is precisely controlled such that the rotor rolls precisely along the stator.
When used as a motor, the unsecured part or rotor produces a rotor driving motion The driving motion of the rotor is quite complex in that it is simultaneously rotating and moving transversely with respect to the stator. One complete rotation of the rotor will result in a movement of the rotor from one side of the stator to the other side and back. The true center of the rotor will of course rotate with the rotor. However, the rotation of the true center of the rotor traces a circle progressing in the opposite direction to the rotation of the rotor, but with the same speed (i.e., reverse orbit) Again, optimum performance is obtained when movement of the rotor is precisely controlled. One complete rotation of the rotor will result in one complete rotation of the true center of the rotor in the opposite direction. Thus, the rotor driving motion is simultaneously a rotation, an oscillation, and a reverse orbit. For multi-lobe motors the reverse orbit is a multiple of the rotational speed, e.g., if a three lobe motor is used the reverse orbit is three times as great as the rotational speed.
Examples of progressive cavity motor and pump devices are well known in the art. The construction and operation of such devices may be readily seen in U.S. Pat. Nos. 3,627,453 to Clark (1971); 2,028,407 to Moineau (1936); 1,892,217 to Moineau (1932) and 4,080,115 to Sims et al. (1978).
Despite the simple construction of progressive cavity devices, use of the devices as motors in driving and drilling apparatus have proven difficult. This difficulty results primarily from the failure to provide a drive train capable of handling the complex rotor driving motion (described above) in a durable, reliable and inexpensive manner. This is further complicated because the drive train must handle large torques.
Of course, there are many known couplings which involve an orbiting member. For example, in U.S. Pat. No. 3,242,644 there is disclosed a torque transmitting device which is made up of three rotary members and two sets of at least three link members journaled in sleeve bearings fixed to the rotary members. Each link member is in the form of two integrally connected axially offset shaft sections. However, such couplings have not heretofore been adapted to progressive cavity devices.
Attempts have been made to convert the complex rotor motion into rotational motion for driving or driven drilling. Of the couplings which have been used in progressive cavity devices, the most commercially successful has been a universal joint attached to the driving or driven end of the rotor and connected to a universal joint attached to the driven drill shaft or pump driving shaft. This approach suffers from several disadvantages, particularly in the area of reliability. For instance, the universal joint tends to fail quickly if run in abrasive environments. The fluids used in progressive cavity drilling apparatus often are or quickly become abrasive Additionally, the universal joint does not control rotor location Generally, the universal joint simply follows the motion of the rotor and does not precisely control the rotor. Consequently, the rotor motion within the stator is somewhat imprecise or sloppy. This causes fluid leakage and power loss. Moreover, a universal joint can only accommodate a certain amount of misalignment per unit length. A universal joint which is long enough to accommodate rotor motion adds significantly to the length of the drilling motor and thereby restricts the ability to drill directionally.
Other known progressive cavity devices employ couplings which are complex and expensive For instance, the aforementioned Sims et al. patent discloses an arrangement providing means directly connecting the rotational and reverse orbiting motion of the rotor to a rotational motion substantially about a single axis whereby the two motions are at different speeds. The connecting means is attached to the rotor and at least a portion of the connecting means is aligned with the true center of the rotor for rotation substantially about the single axis. When the progressive cavity device is used as a motor for drilling, the connecting means attached to the rotor converts the driving motion of the rotor into slower rotational driving motion substantially about a single axis. In some instances, the variation in speed and complexity of this design can cause problems in terms of reliability and durability. Moreover, Sims et al. uses gears to transmit torque; these gears are relatively expensive and can cause friction associated energy loss unless carefully lubricated and maintained.